This application is based upon application No. 2001-13048 filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a drive mechanism employing an electromechanical transducer and a method for controlling the drive mechanism, and more particularly to the drive mechanism which uses a piezoelectric element or another electromechanical transducer, such as the drive mechanism which is preferably used for driving a lens mechanism for a camera, or a precision stage and the method for controlling the drive mechanism.
2. Description of the Related Arts
Japanese Non-examined Laid-Open Patent Publication No. 5-151580 discloses a frictional force reduction mechanism using a piezoelectric element. The publication teaches a technique in which a linear motor is used for driving an optical head in an optical disk apparatus, and the frictional force reduction mechanism is used in a guiding portion of the motor.
In the disclosed technique, a separate actuator is employed for moving a moving body, and hence the production cost increases, and the extra space is necessary.
Accordingly, it is an object of the present invention to provide a drive mechanism employing an electromechanical transducer, in which a frictional force can be controlled by a simple configuration. Also, it is another object of the present invention to provide a method for controlling the drive mechanism.
In order to achieve the above object, according to one aspect of the present invention, there is provided a drive mechanism, comprising: an electromechanical transducer having a pair of ends in an extending and contracting direction; a drive member fixed to one of the pair of ends of the electromechanical transducer; a driven member which is driven by the drive member and which contacts frictionally with the drive member under a predetermined frictional force exerting therebetween; and a controller for supplying the electromechanical transducer with drive pulses, wherein the controller includes a driving circuit which generates a first set of the drive pulses for driving the driven member, and includes a frictional force reducing circuit which generates a second set of the drive pulses for reducing a frictional force exerting between the drive member and the driven member.
In the above configuration, for example, a piezoelectric element, an electrostriction element, or the like may be used as the electromechanical transducer. The first set of driving pulses which is generated by the driving circuit is applied to the electromechanical transducer to extend and contract the electromechanical transducer, whereby the drive member is driven at different velocities depending on the direction to move the driven member which contacts frictionally with the drive member under a predetermined frictional force, along the drive member. On the other hand, the second set of driving pulses which is generated by the frictional force reduction circuit is similarly applied to the electromechanical transducer to extend and contract the electromechanical transducer, whereby the drive member is driven, for example, at a substantially same velocity in both the directions, so that the frictional force between the driven member and the drive member can be reduced while preventing the driven member from being substantially moved with respect to the drive member.
According to the configuration, the driven member can be moved or the frictional force can be reduced by a simple structure using a single element. Therefore, the production cost can be lowered, and the space can be reduced.
The drive mechanism of the invention can be specifically configured in various manners as described below.
As an embodiment, the second set of the drive pulses generated by the frictional force reducing circuit have sinusoidal waveforms.
According to the configuration, even when the drive member is moved by supplying the second set of driving pulses which is sinusoidal to the electromechanical transducer, the frictional force with the drive member can be reduced without causing the driven member not to be substantially moved with respect to the drive member. Because of the use of the sinusoidal waveforms, the frictional force reduction circuit can be configured in a relatively simple manner, and the energy loss can be reduced.
As an embodiment, the frictional force reducing circuit is arranged to change at least one of a frequency and an amplitude of the sinusoidal waveforms of the second set of the drive pulses so as to adjust the reducing amount of the frictional force exerting between the drive member and the driven member.
A configuration in which the frequency and/or amplitude of the sinusoidal waveforms are adjustable can be easily realized.
As an embodiment, the drive pulses supplied to the electromechanical transducer by the controller have rectangular waveforms.
According to the configuration, in accordance with the duty ratio of the rectangular waveforms, for example, the drive member can be driven at different velocities depending on the direction, or the drive member can be driven at a substantially same velocity in both the directions. Therefore, the driven member can be moved, or the frictional force between the driven member and the drive member can be reduced.
As an embodiment, the drive pulses supplied to the transducer by the controller have rectangular waveforms, and the controller is arranged to change a duty ratio of the rectangular waveforms thereof, so that the controller is allowed to drive the driven member and to reduce the frictional force exerting between the drive member and the driven member.
According to the configuration, the effect of reducing the frictional force can be selected by adequately adjusting the duty ratio of the rectangular driving pulses. When the duty ratio is switched over at intervals of several periods, for example, the frictional force can be reduced more effectively. Furthermore, the driving circuit can be used also as the frictional force reduction circuit.
Moreover, a lever device such as a control lever or a joy stick in which a lever member may be driven by using the driving device of the invention is provided.
Usually, a lever member must be held to the same position unless the member is operated, and is requested to be smoothly moved when the lever is to be operated. In some lever members, the holding force and the operational feeling during an operation process are requested to appear in different manners depending on the situation. In some cases, the lever member is requested to be automatically operated.
According to the configuration, the state of the driven member is changed into movement, frictional force reduction, or fixation by changing the driving pulses which is supplied by the controller, whereby automatic/manual/stop modes of the lever member can be easily switched over.
As an embodiment, the drive mechanism further comprises a charge mechanism in which a spring extending and contracting in a moving direction of the driven member is disposed, and in which the spring is charged by movement of the driven member.
According to the configuration, the driven member serves also as the charge mechanism, and hence the space for the device can be reduced. The spring may be precharged by movement of the driven member. When a moving body is to be moved in the opposite direction, the force of the spring can be used in addition to the operation of the drive mechanism, whereby a high-speed movement of the driven member can be realized.
As an embodiment, the drive mechanism can be used for driving a shutter mechanism.
For example, a shutter of a camera is requested to quickly respond in a shutter releasing process. When a shutter mechanism is realized by mechanical means, a delay of several tens to several hundreds of milliseconds is inevitably produced. According to the configuration described above, it is possible to configure a shutter mechanism which can respond without producing a time lag as described above. Moreover, the shutter speed can be enhanced.
In order to achieve the above object, according to another aspect of the present invention, there is provided a drive controlling method for controlling a drive mechanism which comprises: an electromechanical transducer having a pair of ends in an extending and contracting direction; a drive member fixed to one of the pair of ends of the electromechanical transducer; and a driven member which is driven by the drive member and which contacts frictionally with the drive member under a predetermined frictional force exerting therebetween, the drive controlling method comprising the steps of: generating drive pulses; and supplying the electromechanical transducer with the drive pulses, wherein a mode in which the driven member is moved, a mode in which a frictional force between the driven member and the drive member is reduced, and a mode in which the driven member rests relative to the drive member are switched over by changing waveforms of the drive pulses.
According to the method, the driving of the driven member, and the frictional force between the driven member and the drive member can be controlled by changing waveforms of the driving pulses.
As an embodiment, the drive pulses have sinusoidal waveforms.
As an embodiment, the reducing amount of a frictional force exerting between the drive member and the driven member is adjusted by changing at least one of the frequency and the amplitude of the sinusoidal waveforms of the drive pulses.
As an embodiment, the drive pulses have rectangular waveforms.
As an embodiment, a duty ratio of the rectangular waveforms of the drive pulses is changed so as to drive the driven member and so as to reduce a frictional force exerting between the drive member and the driven member.
According to the embodiment, the driving of the driven member, and the frictional force between the driven member and the drive member can be controlled by changing the duty ratio of the rectangular driving pulses.